A variety of means have been used to blend soluble additives into fluid streams. These include positive displacement metering pumps, venturi tubes, pumps and control valves, gravity feed drainage and batch mixing. Specifically in the area of water soluble additives for garden type of application, a venturi type of suction device attached to a jar at the end of a garden hose is commonly used. Attached to the fluid suction point typically is a tube to the bottom of the jar, which slowly drains the additive from the jar.
Several problems occur with this type of garden additive system. The rate of addition is not constant since the height of additive (hydraulic head) is changing as additive is withdrawn. Blending and mixing efficiency also varies as fluid is withdrawn and pressure at the suction point changes. The configuration also requires the use of a garden hose even if a sprinkler system is in place and operating. The size of the jar is limited since it must be held for long times, sometimes necessitating multiple fillings of the jar for a single application. Leakage around fittings can also contaminate operator and equipment. Residue in the jar must also be flushed and cleaned out after each use to prevent encrustation. Line pressure surges may also present a safety hazard to someone holding a glass jar. At all times, the operation must be manned and monitored in order to distribute the blended discharge and end the application when the jar is empty.
Other types of additive systems (pumps, valves, etc.) are generally too cumbersome, complex, unreliable or costly for the simple gardening task. What has been sought is a simple, reliable means of supplying a fixed amount of insecticide or liquid fertilizer in a timed sprinkler system or garden hose application.